1. Field of Invention
The present invention relates to a planetary gear unit used in an automatic transmission. In particular, the present invention relates to a structure for positioning and supporting a clutch member coupled with one element of a planetary gear and engaging a clutch drum, and to friction disks for frictionally engaging a clutch drum.
2. Description of Related Art
Planetary gear units are commonly used in automatic transmissions. For example, a planetary gear unit is used as a forward-reverse switching mechanism for switching between forward travel and travel in reverse using a belt type continuously variable transmission (hereinafter referred to as xe2x80x9cCVTxe2x80x9d).
FIG. 6 shows in cross-sectional view, a conventional planetary gear unit 100 as including planetary gearing 200, a clutch for forward (hereinafter referred to as xe2x80x9cforward clutch C1xe2x80x9d) and a brake B1 for reverse (hereinafter referred to as xe2x80x9creverse brake B1xe2x80x9d). The planetary gearing 200 includes a sun gear S, a ring gear R, a carrier CR, and a pinion P supported by the carrier CR and meshing with both the ring gear R and the sun gear S, all of which members are disposed around an input shaft 103.
A hydraulic actuator 111 for operation of the forward clutch C1 has a clutch drum 109, a piston member 112, a return spring 113, and the like. Furthermore, a hydraulic actuator 123 for operation of the reverse brake B1 is formed in a partition wall portion of a case 106, and further includes a piston member 124, a return spring 125, and the like.
The aforementioned input shaft 103 is coupled both to an output portion of a torque converter (not shown) and to the clutch drum 109. The ring gear R is axially positioned and supported (in the direction indicated by the arrows A-B in FIG. 6) by being sandwiched between two snap rings 240 and 241 and is splined to an end hub portion of the clutch drum 109. A pressure receiving member 244 of the outer friction disks 116 of the forward clutch C1 is axially positioned and supported (in the direction indicated by the arrows A-B in FIG. 6) (sandwiched) by a snap ring 242 and splining with the interior surface of an end hub portion of the clutch drum 109.
Inner friction disks 117 of the forward clutch C1 are splined to an end hub portion of disk member 114. The disk member 114 has its inner peripheral portion fixed to the sun gear S. In addition, the sun gear S is splined to the primary pulley 105.
Outer friction disks 118 of the reverse brake B1 are splined to the aforementioned case 106. Furthermore, inner friction disks 119 of the reverse brake B1 are splined to the outer surface of an end hub portion of a side disk 230 which is one portion of the planetary carrier CR.
With a planetary gear unit as described above, if working pressure is applied to the hydraulic actuator 111 of the forward clutch C1, the piston member 112 slides in the direction indicated by the arrow A in FIG. 6, against the force of the return spring 113. Thus, the outer friction disks 116 and the inner friction disks 117 of the forward clutch C1 are forced together so that they become engaged by frictional force. As a result, the input rotation of the clutch drum 109 engaged with the aforementioned input shaft 103 is transmitted to the primary pulley 105 via the forward clutch C1, the disk member 114 and the sun gear S. Accordingly, if the forward clutch C1 is engaged and the reverse brake B1 is released, the torque of the input shaft 103 is output as normal (forward) rotation of the primary pulley 105.
Furthermore, if working pressure is applied to the hydraulic actuator 123 of the reverse brake B1, piston member 124 is forced to slide in the direction indicated by the arrow A in FIG. 6, against the force of a return spring 125. Thus, the outer friction disks 118 and the inner friction disks 119 of the reverse brake B1 are forced together so that they become engaged by frictional force. As a result, the carrier CR is fixed with respect to the case 106 via the reverse brake B1. The input rotation of the clutch drum 109, engaged with the input shaft 103, is transmitted as reverse rotation to the primary pulley 105, via the ring gear R, the carrier CR fixed with respect to the case 106, and the sun gear S. Accordingly, if the reverse brake B1 is engaged and the forward clutch C1 is released, the torque of the input shaft 103 is output as reverse rotation to the primary pulley 105.
However, with the aforementioned planetary gear unit 100, in order to axially position and support the ring gear R and the pressure receiving member 244 relative to the clutch drum 109, three snap rings 240, 241 and 242 are utilized. This configuration does not allow for cost savings which might otherwise be attainable through reduction of parts. Moreover, a configuration in which the snap rings 241 and 242 are disposed between the ring gear R and the forward clutch C1, leads to design problems related to strength and assembly. In other words, space is required for receiving the snap rings 241 and 242, which impedes making the overall planetary gear unit 100 more axially compact.
Accordingly, it is an object of the present invention to provide a planetary gear unit that can solve the problems mentioned above. This is accomplished by axially positioning and supporting the friction disks of the clutch relative to the clutch drum using a first stopper member. Furthermore, an engaging member coupled with one element of the planetary gear is axially positioned and supported by being sandwiched between the first stopper member and a second stopper member.
A planetary gear unit according to one embodiment of the present invention is provided with planetary gearing and a clutch having a clutch drum disposed adjacent to the planetary gearing. The planetary gearing includes: an engaging member which is coupled with one element of the planetary gearing and is engaged with an interior surface of the clutch drum; a first stopper member axially positioning and supporting friction disks of the clutch and disposed on the interior surface of the clutch drum; and a second stopper member axially positioning and supporting the aforementioned engaging member and also disposed on the internal surface of the clutch drum. The planetary gear unit has the engaging member sandwiched between the first stopper member and the second stopper member, thus axially positioning and supporting the engaging member.
In the first embodiment of the present invention, the friction disks are axially positioned and supported by the first stopper member and the engaging member is axially positioned and supported by being sandwiched between the first stopper member and the second stopper member. Accordingly, it is possible to save cost by reducing the number of parts. Furthermore, since the friction disks (in particular, a pressure receiving portion thereof) are axially positioned and supported by the first stopper member, and the engaging member is axially positioned and supported by being sandwiched between the first stopper member and the second stopper member, the spacing between the friction disks and the engaging member is only that which is necessary for provision of the first stopper member. Accordingly, the space between the engaging member and the friction disks (in particular, the pressure receiving portion thereof) is small, and it is possible to make the entire planetary gear unit more axially compact.
Preferably, the aforementioned clutch drum has a toroidal recess in its internal peripheral surface, and the first stopper member is a tapered snap ring having a tapered surface abutting against a corner portion of the recess and an abutting surface that abuts against an inner surface of the recess.
The tapered snap ring (xe2x80x9cfirst stopper memberxe2x80x9d) fits into the toroidal recess formed in the internal surface of the clutch drum without any clearance. As a result, it is possible to maintain highly accurate positioning of the friction disks of the clutch and the engaging member. Moreover, the tapered snap ring can maintain highly accurate positioning of the friction disks of the clutch even as pressure is received from the hydraulic servo of the clutch. Accordingly, it is possible to execute highly accurate hydraulic control of the clutch. In addition, it is also possible to maintain highly accurate positioning of the friction disks of the clutch even when the clutch is disengaged. As a result, it is possible to maintain the spacing between the friction disks of the clutch with a high degree of accuracy, thus preventing any contact between the friction disks which, in turn, prevents unwanted wear and seizure of the friction disks.
The abutting surface of the aforementioned tapered snap ring is disposed facing the engaging member. As a result, it is possible to maintain the position of the tapered snap ring with a high degree of accuracy even when pressure is received from the hydraulic servo of the clutch. Accordingly, it is possible to maintain the axial positioning of the friction disks and the engaging member and to execute stable and highly accurate hydraulic control of the clutch.
The planetary gear unit of the present invention preferably has the aforementioned engaging member provided with an axially extending protrusion located radially inward of the tapered snap ring, thus preventing the first stopper member from slipping out from the clutch drum. The planetary gear unit according to the third embodiment is otherwise like one of the first and second embodiments of the present invention.
The planetary gear unit of the present invention preferably has planetary gearing which includes helical gears. Although the helical gears make it possible to reduce gear noise of the planetary gearing, the helical gears also generate thrust force. However, since the first stopper member and the second stopper member axially position the engaging member, the positions of the engaging member and the friction disks are maintained with a high degree of accuracy. Furthermore, in particular, if the first stopper member is a tapered snap ring, it is possible to maintain the axial positions of the engaging member and the friction disks with an even greater degree of accuracy.
A fifth embodiment of the present invention is the planetary gear unit of the present invention which has its planetary gearing configured such that no thrust force is generated by the helical gears when the clutch is engaged. Generation of thrust forced in the first stopper member is prevented by coupling the engaging member with one element of the planetary gearing. Accordingly, it is possible to avoid affecting the axial positioning and support of the friction disks of the clutch and, as a result, it is possible to provide highly accurate hydraulic control of the clutch.
The one rotary element of the planetary gearing to which the engaging member is coupled may be a ring gear. In this configuration the engaging member is fixed to the ring gear and extends radially outward into engagement with the internal surface of the clutch drum. As a result, it is possible to axially position and support the engaging member and the ring gear with a high degree of accuracy relative to the clutch drum.
Alternatively, the one rotary element of the planetary gearing to which the engaging member is coupled is a sun gear. In this configuration, the engaging member is fixed to a sun gear and extends radially out from the sun gear into engagement with the internal surface of the clutch drum. As a result, it is possible to axially position and support the engaging member with a high degree of accuracy relative to the clutch drum.
The terminology xe2x80x9cfixed toxe2x80x9d as used herein means an integral construction, as shown for elements R and 4 in FIG. 1, an attachment as shown for elements S and 470 in FIG. 5, or any other type of direct coupling which causes the engaging member to rotate with the rotary element of the planetary gearing to which it is directly coupled or xe2x80x9cfixed.xe2x80x9d
The planetary gear unit of the present invention may serve as a forward-reverse switching mechanism for switching rotation from a driving source between normal (forward) rotation and reverse rotation, which rotation is then transmitted to the drive wheels. As a result, it is possible to reduce costs by reducing number of parts, and furthermore, to provide a forward-reverse mechanism for switching between normal rotation and reverse rotation which is axially compact.